Rapid production apparatus (RPAs) form objects by sequentially forming thin layers, hereinafter “construction layers”, of a material one on top of the other responsive to data, hereinafter “construction data”, defining the objects. There are numerous and varied types of RPAs and different methods by which they form the thin construction layers they use to build an object.
One type of RPA, conventionally referred to as an “ink-jet RPA”, “prints” each layer of an object it builds. To form a given layer the ink-jet RPA controls. at least one dispenser, referred to as a “printing head”, to dispense at least one construction material in liquid form in a pattern responsive to construction data for the object and then solidifies the dispensed material. At least one construction material, hereinafter a “building material” (BM), dispensed to form the layer is printed in the shape of a cross section of the object. Building material in adjacent construction layers is printed in the shape of thin cross sections of the object that are displaced relative to each other by a small incremental distance along a same direction, hereinafter referred to as a “stacking direction”, relative to the object.
For convenience of exposition, the cross sections of the object in whose shapes the construction layers are formed are assumed to be parallel to the xy-plane of a suitable coordinate system and the stacking direction is in the z-direction of the coordinate system. Optionally, the building material is a photopolymer, which is hardened after deposition by exposure to suitable electromagnetic radiation, typically UV radiation.
For many construction objects, because of the complexity and/or shape of the objects, construction layers comprising only BM printed in the shape of cross sections of the construction objects are not completely self-supporting and require support during construction of the object. For such cases, at least one construction material, hereinafter referred to as “support material” (SM), is printed as required in suitable regions of each layer. to provide support for the building material in the layer. The support material and/or a shape in which it is formed, is such that upon completion of the object it can be removed from the object without substantially damaging the building material. In some embodiments, the support material, like the building material, is also a photopolymer.
An ink-jet type of RPA typically comprises at least one ink-jet printing head comprised in a “printing head block”, which is mounted to a “shuttle”. Each printing head has an array of one or more output orifices and is controllable to dispense construction material from each orifice independently of dispensing construction material from the other orifices. The construction material comprises one or more types of photopolymer materials typically stored in at least one cartridge from which a suitable configuration of pipes transports the material or materials to one or more reservoirs in the printing head block from which the printing head receives the material . Optionally, to maintain appropriate viscosity of the at least one photopolymer, a controller controls at least one heater, optionally mounted to the printing block, print head and/or reservoir, to heat the photopolymer to a suitable operating temperature. The one or more types of photopolymers may, generally, be dispensed in any combination, separately or together, simultaneously or consecutively.
During construction of an object, a controller controls the shuttle to repeatedly move over a support surface, hereinafter a “construction platform”, parallel to the xy-plane. As the shuttle moves, the controller controls each printing head to dispense construction material selectively through its orifices responsive to construction data defining the object to print the construction layers from which the object is made on the construction platform, one layer after the other, one on top of the other. Mounted to the shuttle, adjacent to the printing head block are one or more sources of electromagnetic radiation, optionally UV radiation, for curing the photopolymer construction material printed in each construction layer. Also, optionally, mounted to the shuttle adjacent to the at least one printing head block is a “leveling roller” which levels newly printed layers of construction material to a predetermined layer height by removing surplus material and/or peaks of material in the layer. The surplus material removed from the layer is wiped off the roller by a “cleaning wiper” and gathered in a waste container comprised in the shuttle.
Optionally, in moving the shuttle over the support surface during production of a construction layer, the controller controls the shuttle to move back and forth along the x-direction. Optionally, at any one or more reversals of the shuttle along the x-direction the controller increments displacement of the shuttle in the y-direction. Following production of a given construction layer, either the construction platform is lowered or the shuttle raised, along the stacking direction by a distance equal to a thickness of a next construction layer to be produced over the just formed given layer.
During construction of an object, excess cured photopolymer construction material has a tendency to accumulate on or between the at least one printing head in the printing head block and on the cleaning wiper. The accumulated material may result in total or partial blockage of output orifices, generating inaccuracies in deposition of construction material and/or damage to a printed layer as the printing heads and roller move over a printed layer. Often, functioning of a printing head block may be so degraded by accumulated photopolymer “debris” that the printing block must be replaced. Replacing a printing head block is generally expensive, time consuming, and requires recalibration of the RPA so that deposition of polymer via the output orifices can be accurately controlled.
Configurations of ink-jet type RPAs are described in U.S. Pat. Nos. 6,259,962, 6,658,314, 6,569,373 and US applications Ser. Nos. 10/101,089, 09,484,272, 10/336,032, the disclosures of which are incorporated herein by reference.